Acidic pH-Responsive siRNA Conjugate for Reversible Carrier Stability and Accelerated Endosomal Escape with Reduced IFNα-Associated Immune Response

Visualizing the cellular internalization of therapeutic antibodies via pH-sensitive release of AIEgen

Among the fastest-growing bio-pharmaceuticals, therapeutic antibodies have achieved unprecedented success in treating various diseases. Though powerful, issues such as inefficacy or acquired resistance are waiting to be addressed to benefit more patients with improved therapeutic outcomes. In addition to in vivo distribution, the cellular spatiotemporal information including the antibody-antigen interaction and subsequent internalization is found to be important for the therapeutic effects. To better understand the cellular fate of therapeutic antibodies, especially the cellular internalization process, we employed a pH-sensitive linker to attach a red-emissive AIEgen onto the antibody. The resulting antibody conjugate will undergo AIEgen release to liberate brilliant fluorescence inside acidic endo/lysosomes, allowing wash-free visualization of the internalization process and facilitating the evaluation of antibody-drug efficacy.

A convenient protonated strategy for constructing nanodrugs from hydrophobic drug-inhibitor conjugates to reverse tumor multidrug resistance

Combination therapy has proven effective in counteracting tumor multidrug resistance (MDR). However, the pharmacokinetic differences among various drugs and inherent water insolubility for most small molecule agents greatly hinder their synergistic effects, which makes the delivery of drugs for combination therapy in vivo a key problem. Herein, we propose a protonated strategy to transform a water-insoluble small molecule drug-inhibitor conjugate into an amphiphilic one, which then self-assembles into nanoparticles for co-delivery in vivo to overcome tumor MDR. Specifically, paclitaxel (PTX) is first coupled with a third-generation P-glycoprotein (P-gp) inhibitor zosuquidar (Zos) through a glutathione (GSH)-responsive disulfide bond to produce a hydrophobic drug-inhibitor conjugate (PTX-ss-Zos). Subsequently treated with hydrochloric acid ethanol solution (HCl/EtOH), PTX-ss-Zos is transformed into the amphiphilic protonated precursor and then forms nanoparticles (PTX-ss-Zos@HCl NPs) in water by molecular self-assembly. PTX-ss-Zos@HCl NPs can be administered intravenously and accumulated specifically at tumor sites. Once internalized by cancer cells, PTX-ss-Zos@HCl NPs can be degraded under the overexpressed GSH to release PTX and Zos simultaneously, which synergistically reverse tumor MDR and inhibit tumor growth. This offers a promising strategy to develop small molecule self-assembled nanoagents to reverse tumor MDR in combination therapy.

Recent Progress in Nucleic Acid Pulmonary Delivery toward Overcoming Physiological Barriers and Improving Transfection Efficiency

Pulmonary delivery of therapeutic agents has been considered the desirable administration route for local lung disease treatment. As the latest generation of therapeutic agents, nucleic acid has been gradually developed as gene therapy for local diseases such as asthma, chronic obstructive pulmonary diseases, and lung fibrosis. The features of nucleic acid, specific physiological structure, and pathophysiological barriers of the respiratory tract have strongly affected the delivery efficiency and pulmonary bioavailability of nucleic acid, directly related to the treatment outcomes. The development of pharmaceutics and material science provides the potential for highly effective pulmonary medicine delivery. In this review, the key factors and barriers are first introduced that affect the pulmonary delivery and bioavailability of nucleic acids. The advanced inhaled materials for nucleic acid delivery are further summarized. The recent progress of platform designs for improving the pulmonary delivery efficiency of nucleic acids and their therapeutic outcomes have been systematically analyzed, with the application and the perspectives of advanced vectors for pulmonary gene delivery.

Covalent Polymer-RNA Conjugates for Potent Activation of the RIG-I Pathway

RNA ligands of retinoic acid-inducible gene I (RIG-I) are a promising class of oligonucleotide therapeutics with broad potential as antiviral agents, vaccine adjuvants, and cancer immunotherapies. However, their translation has been limited by major drug delivery barriers, including poor cellular uptake, nuclease degradation, and an inability to access the cytosol where RIG-I is localized. Here this challenge is addressed by engineering nanoparticles that harness covalent conjugation of 5'-triphospate RNA (3pRNA) to endosome-destabilizing polymers. Compared to 3pRNA loaded into analogous nanoparticles via electrostatic interactions, it is found that covalent conjugation of 3pRNA improves loading efficiency, enhances immunostimulatory activity, protects against nuclease degradation, and improves serum stability. Additionally, it is found that 3pRNA could be conjugated via either a disulfide or thioether linkage, but that the latter is only permissible if conjugated distal to the 5'-triphosphate group. Finally, administration of 3pRNA-polymer conjugates to mice significantly increases type-I interferon levels relative to analogous carriers that use electrostatic 3pRNA loading. Collectively, these studies have yielded a next-generation polymeric carrier for in vivo delivery of 3pRNA, while also elucidating new chemical design principles for covalent conjugation of 3pRNA with potential to inform the further development of therapeutics and delivery technologies for pharmacological activation of RIG-I.

Recent Advances in Engineering Carriers for siRNA Delivery

RNA interference (RNAi) technology has been a promising treatment strategy for combating intractable diseases. However, the applications of RNAi in clinical are hampered by extracellular and intracellular barriers. To overcome these barriers, various siRNA delivery systems have been developed in the past two decades. The first approved RNAi therapeutic, Patisiran (ONPATTRO) using lipids as the carrier, for the treatment of amyloidosis is one of the most important milestones. This has greatly encouraged researchers to work on creating new functional siRNA carriers. In this review, the recent advances in siRNA carriers consisting of lipids, polymers, and polymer-modified inorganic particles for cancer therapy are summarized. Representative examples are presented to show the structural design of the carriers in order to overcome the delivery hurdles associated with RNAi therapies. Finally, the existing challenges and future perspective for developing RNAi as a clinical modality will be discussed and proposed. It is believed that the addressed contributions in this review will promote the development of siRNA delivery systems for future clinical applications.

PLGA nanomedical consignation: A novel approach for the management of prostate cancer

The malignancy of the prostate is a complicated ailment which impacts millions of male populations around the globe. Despite the multitude of endeavour accomplished within this domain, modalities that are involved in the ameliorative management of predisposed infirmity are still relent upon non-specific and invasive procedures, thus imposing a detrimental mark on the living standard of the individual. Also, the orchestrated therapeutic interventions are still incompetent in substantiating a robust and unabridged therapeutic end point owing to their inadequate solubility, low bioavailability, limited cell assimilation, and swift deterioration, thereby muffling the clinical application of these existing treatment modalities. Nanotechnology has been employed in an array of modalities for the medical management of malignancies. Among the assortment of available nano-scaffolds, nanocarriers composed of a bio-decomposable and hybrid polymeric material like PLGA hold an opportunity to advance as standard chemotherapeutic modalities. PLGA-based nanocarriers have the prospect to address the drawbacks associated with conventional cancer interventions, owing to their versatility, durability, nontoxic nature, and their ability to facilitate prolonged drug release. This review intends to describe the plethora of evidence-based studies performed to validate the applicability of PLGA nanosystem in the amelioration of prostate malignancies, in conjunction with PLGA focused nano-scaffold in the clinical management of prostate carcinoma. This review seeks to explore numerous evidence-based studies confirming the applicability of PLGA nanosystems in ameliorating prostate malignancies. It also delves into the role of PLGA-focused nano-scaffolds in the clinical management of prostate carcinoma, aiming to provide a comprehensive perspective on these advancements.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Design, strategies, and therapeutics in nanoparticle-based siRNA delivery systems for breast cancer

Utilizing small interfering RNA (siRNA) as a treatment for cancer, a disease largely driven by genetic aberrations, shows great promise. However, implementing siRNA therapy in clinical practice is challenging due to its limited bioavailability following systemic administration. An attractive approach to address this issue is the use of a nanoparticle (NP) delivery platform, which protects siRNA and delivers it to the cytoplasm of target cells. We provide an overview of design considerations for using lipid-based NPs, polymer-based NPs, and inorganic NPs to improve the efficacy and safety of siRNA delivery. We focus on the chemical structure modification of carriers and NP formulation optimization, NP surface modifications to target breast cancer cells, and the linking strategy and intracellular release of siRNA. As a practical example, recent advances in the development of siRNA therapeutics for treating breast cancer are discussed, with a focus on inhibiting cancer growth, overcoming drug resistance, inhibiting metastasis, and enhancing immunotherapy.

Redox-responsive self-assembled polymeric nanoprodrug for delivery of gemcitabine in B-cell lymphoma therapy

Gemcitabine, as a standard and classic strategy for B-cell lymphoma in the clinic, is limited by its poor pharmacodynamics. Although stimuli-responsive polymeric nanodelivery systems have been widely investigated in the past decade, issues such as complicated procedures, low loading capacity, and uncontrollable release kinetics still hinder their clinical translation. In view of the above considerations, we attempt to construct hyperbranched polyprodrug micelles with considerable drug loading via simple procedures and make use of the particularity of the tumor microenvironment to ensure that the micelles are "inactivated" in normal tissues and "activated" in the tumor microenvironment. Hence, in this work, a redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) with considerable loading capacity (≈ 24.6%) exhibited on-demand and accurate control of gemcitabine release under a simulated tumor microenvironment and thus significantly induced the apoptosis of B-cell lymphoma in vitro. Moreover, in the A20 tumor xenograft murine model, GSP NPs efficiently decreased the expansion of tumor tissues with minimal systemic toxicity. In summary, these redox-responsive and self-assembling GSP NPs with a facile one-pot synthesis procedure may hold great potency in clinical translation for enhanced chemotherapy of B-cell lymphoma. STATEMENT OF SIGNIFICANCE: A redox-responsive polymeric gemcitabine-prodrug (GEM-S-S-PEG) was one-pot synthesized via facile esterification and acylation. The self-assembled subsize (< 100 nm) GEM-S-S-PEG (GSP NPs) exhibited significant tumor therapeutic effects in vitro and in vivo. The polyprodrug GEM-S-S-PEG prepared in this study shows the great potential of redox-responsive nanodrugs for antitumor activity, which provides a reference value for the optimization of the design of functional polyprodrugs.

Tumor microenvironment and nanotherapeutics: intruding the tumor fort

Over recent years, advancements in nanomedicine have allowed new approaches to diagnose and treat tumors. Nano drug delivery systems exploit the enhanced permeability and retention (EPR) effect and enter the tumor tissue's interstitial space. However, tumor barriers play a crucial role, and cause inefficient EPR or the homing effect. Mounting evidence supports the hypothesis that the components of the tumor microenvironment, such as the extracellular matrix, and cellular and physiological components collectively or cooperatively hinder entry and distribution of drugs, and therefore, limit the theragnostic applications of cancer nanomedicine. This abnormal tumor microenvironment plays a pivotal role in cancer nanomedicine and was recently recognized as a promising target for improving nano-drug delivery and their therapeutic outcomes. Strategies like passive or active targeting, stimuli-triggered nanocarriers, and the modulation of immune components have shown promising results in achieving anticancer efficacy. The present review focuses on the tumor microenvironment and nanoparticle-based strategies (polymeric, inorganic and organic nanoparticles) for intruding the tumor barrier and improving therapeutic effects.

Advancing Inorganic Coordination Chemistry by Spectroscopy of Isolated Molecules: Methods and Applications

A unique feature of the work carried out in the Collaborative Research Center 3MET continues to be its emphasis on innovative, advanced experimental methods which hyphenate mass-selection with further analytical tools such as laser spectroscopy for the study of isolated molecular ions. This allows to probe the intrinsic properties of the species of interest free of perturbing solvent or matrix effects. This review explains these methods and uses examples from past and ongoing 3MET studies of specific classes of multicenter metal complexes to illustrate how coordination chemistry can be advanced by applying them. As a corollary, we will show how the challenges involved in providing well-defined, for example monoisomeric, samples of the molecular ions have helped to further improve the methods themselves thus also making them applicable to many other areas of chemistry.

Stimuli-responsive polypeptides for controlled drug delivery

Controlled drug delivery systems, which could release loaded therapeutics upon physicochemical changes imposed by physiological triggers in the desired zone and during the required period of time, offer numerous advantages over traditional drug carriers including enhanced therapeutic effects and reduced toxicity. A polypeptide is a biocompatible and biodegradable polymer, which can be conveniently endowed with stimuli-responsiveness by introducing natural amino acid residues with innate stimuli-responsive characteristics or introducing responsive moieties to its side chains using simple conjugating methods, rendering it an ideal biomedical material for controlled drug delivery. This feature article summarizes our recent work and other relevant studies on the development of polypeptide-based drug delivery systems that respond to single or multiple physiological stimuli (e.g., pH, redox potential, glucose, and hypoxia) for controlled drug delivery applications. The material designs, synthetic strategies, loading and controlled-release mechanisms of drugs, and biomedical applications of these stimuli-responsive polypeptides-based drug delivery systems are elaborated. Finally, the challenges and opportunities in this field are briefly discussed.

The targetable nanoparticle BAF312@cRGD-CaP-NP represses tumor growth and angiogenesis by downregulating the S1PR1/P-STAT3/VEGFA axis in triple-negative breast cancer

Background

Overexpressed vascular endothelial growth factor A (VEGFA) and phosphorylated signal transducer and activator of transcription 3 (P-STAT3) cause unrestricted tumor growth and angiogenesis of breast cancer (BRCA), especially triple-negative breast cancer (TNBC). Hence, novel treatment strategy is urgently needed.

Results

We found sphingosine 1 phosphate receptor 1 (S1PR1) can regulate P-STAT3/VEGFA. Database showed S1PR1 is highly expressed in BRCA and causes the poor prognosis of patients. Interrupting the expression of S1PR1 could inhibit the growth of human breast cancer cells (MCF-7 and MDA-MB-231) and suppress the angiogenesis of human umbilical vein endothelial cells (HUVECs) via affecting S1PR1/P-STAT3/VEGFA axis. Siponimod (BAF312) is a selective antagonist of S1PR1, which inhibits tumor growth and angiogenesis in vitro by downregulating the S1PR1/P-STAT3/VEGFA axis. We prepared pH-sensitive and tumor-targeted shell-core structure nanoparticles, in which hydrophilic PEG2000 modified with the cyclic Arg-Gly-Asp (cRGD) formed the shell, hydrophobic DSPE formed the core, and CaP (calcium and phosphate ions) was adsorbed onto the shell; the nanoparticles were used to deliver BAF312 (BAF312@cRGD-CaP-NPs). The size and potential of the nanoparticles were 109.9 ± 1.002 nm and − 10.6 ± 0.056 mV. The incorporation efficacy for BAF312 was 81.4%. Results confirmed BAF312@cRGD-CaP-NP could dramatically inhibit tumor growth and angiogenesis in vitro and in MDA-MB-231 tumor-bearing mice via downregulating the S1PR1/P-STAT3/VEGFA axis.

Conclusions

Our data suggest a potent role for BAF312@cRGD-CaP-NPs in treating BRCA, especially TNBC by downregulating the S1PR1/P-STAT3/VEGFA axis.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00904-6.

Caveolae-Mediated Endocytosis Drives Robust siRNA Delivery of Polymeric Nanoparticles to Macrophages

Cytosolic delivery of small interfering RNA (siRNA) remains challenging, and a profound understanding of the cellular uptake and intracellular processing of siRNA delivery systems could greatly improve the development of siRNA-based therapeutics. Here, we show that caveolae-mediated endocytosis (CvME) accounts for the robust siRNA delivery of mannose-modified trimethyl chitosan-cysteine/tripolyphosphate nanoparticles (MTC/TPP NPs) to macrophages by circumventing lysosomes. We show that the Golgi complex and ER are key organelles required for the efficient delivery of siRNA to macrophages in which the siRNA accumulation positively correlates with its silencing efficiency (r = 0.94). We also identify syntaxin6 and Niemann-Pick type C1 (NPC1) as indispensable regulators for MTC/TPP NPs-delivered siRNA into macrophages both in vitro and in vivo. Syntaxin6 and NPC1 knockout substantially decrease the cellular uptake and gene silencing of the siRNA delivered in MTC/TPP NPs in macrophages, which result in poor therapeutic outcomes for mice bearing acute hepatic injury. Our results suggest that highly efficient siRNA delivery can be achieved via CvME, which would give ideas for designing optimal delivery vectors to facilitate the clinical translation of siRNA drugs.

Polypeptide-based drug delivery systems for programmed release

Recent years have seen increasing interests in the use of ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs) to prepare synthetic polypeptides, a class of biocompatible and versatile materials, for various biomedical applications. Because of their rich side-chain functionalities, diverse hydrophilicity/hydrophobicity profiles, and the capability of forming stable secondary structures, polypeptides can assemble into a variety of well-organized nano-structures that have unique advantages in drug delivery and controlled release. Herein, we review the design and use of polypeptide-based drug delivery system derived from NCA chemistry, and discuss the future perspectives of this exciting and important biomaterial area that may potentially change the landscape of next-generation therapeutics and diagnosis. Given the high significance of precise control over release for polypeptide-based systems, we specifically focus on the versatile designs of drug delivery systems capable of programmed release, through the changes in the chemical and physical properties controlled by the built-in molecular structures of polypeptides.

pH-Responsive Charge-Conversion Progelator Peptides

A simple strategy for generating stimuli-responsive peptide-based hydrogels via charge-conversion of a self-assembling peptide (SAP) is described. These materials are formulated as soluble, polyanionic peptides, containing maleic acid, citraconic acid, or dimethylmaleic acid masking groups on each lysine residue, which do not form assemblies, but instead flow easily through high gauge needles and catheters. Acid-induced mask hydrolysis renews the zwitterionic nature of the peptides with concomitant and rapid self-assembly via β-sheet formation into rehealable hydrogels. The use of different masks enables one to tune pH responsiveness and assembly kinetics. In anticipation of their potential for in vivo hydrogel delivery and use, progelators exhibit hemocompatibility in whole human blood, and their peptide components are shown to be noncytotoxic. Finally, demonstration of stimuli-induced self-assembly for dye sequestration suggests a simple, non-covalent strategy for small molecule encapsulation in a degradable scaffold. In summary, this simple, scalable masking strategy allows for preparation of responsive, dynamic self-assembling biomaterials. This work sets the stage for implementing biodegradable therapeutic hydrogels that assemble in response to physiological, disease-relevant states of acidosis.

Cyclic Anhydrides as Powerful Tools for Bioconjugation and Smart Delivery

Cyclic anhydrides are potent tools for bioconjugation; therefore, they are broadly used in the functionalization of biomolecules and carriers. The pH-dependent stability and reactivity, as well as the physical properties, can be tuned by the structure of the cyclic anhydride used; thus, their application in smart delivery systems has become very important. This review intends to cover the last updates in the use of cyclic anhydrides as pH-sensitive linkers, their differences in reactivity, and the latest applications found in bioconjugation chemistry or chemical biology, and when possible, in drug delivery.

Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability

Herein, we describe capsule polymer particles with precisely controlled pH-responsive release properties prepared directly via the interfacial photo-cross-linking of spherical poly(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P(DEAEMA-CEMA)) particles. In the interfacial photo-cross-linking, photoreactive cinnamoyl groups in the polymer particles were cross-linked via [2π + 2π] cycloaddition reactions at the polymer/water interface, showing that the shell-cross-linked hollow polymer particles can be directly prepared from spherical polymer particles. The approach has fascinating advantages such as using minimal components, simplicity, and not requiring sacrificial template particles and toxic solvents. The following important observations are made: (I) encapsulated materials were stably retained in the capsule particles under neutral pH conditions; (II) encapsulated materials were released from the capsule particles under acidic pH conditions; (III) the release kinetics of encapsulated materials were controlled by the pH conditions; i.e., immediate and sustained release was achieved by varying the acidity of the aqueous media; (IV) the photoirradiation time did not significantly affect the release kinetics under different pH conditions; and (V) the pH-responsive release properties were regulated by changing the polymer composition in P(DEAEMA-CEMA). Furthermore, by exploiting the pH-responsiveness, capsule particles are successfully obtained via an all-aqueous process from spherical polymer particles. The advantages of the all-aqueous encapsulation process allowed the water-soluble biomacromolecules such as DNA and saccharides to be successfully encapsulated in the P(DEAEMA-CEMA) hollow particles. With this simple interfacial photo-cross-linking strategy, we envision the ready synthesis of sophisticated particulate materials for broad application in advanced research fields.

Harnessing Endogenous Stimuli for Responsive Materials in Theranostics

Materials that respond to endogenous stimuli are being leveraged to enhance spatiotemporal control in a range of biomedical applications from drug delivery to diagnostic tools. The design of materials that undergo morphological or chemical changes in response to specific biological cues or pathologies will be an important area of research for improving efficacies of existing therapies and imaging agents, while also being promising for developing personalized theranostic systems. Internal stimuli-responsive systems can be engineered across length scales from nanometers to macroscopic and can respond to endogenous signals such as enzymes, pH, glucose, ATP, hypoxia, redox signals, and nucleic acids by incorporating synthetic bio-inspired moieties or natural building blocks. This Review will summarize response mechanisms and fabrication strategies used in internal stimuli-responsive materials with a focus on drug delivery and imaging for a broad range of pathologies, including cancer, diabetes, vascular disorders, inflammation, and microbial infections. We will also discuss observed challenges, future research directions, and clinical translation aspects of these responsive materials.

100th Anniversary of Macromolecular Science Viewpoint: Attractive Soft Matter: Association Kinetics, Dynamics, and Pathway Complexity in Electrostatically Coassembled Micelles

Electrostatically coassembled micelles constitute a versatile class of functional soft materials with broad application potential as, for example, encapsulation agents for nanomedicine and nanoreactors for gels and inorganic particles. The nanostructures that form upon the mixing of selected oppositely charged (block co)polymers and other ionic species greatly depend on the chemical structure and physicochemical properties of the micellar building blocks, such as charge density, block length (ratio), and hydrophobicity. Nearly three decades of research since the introduction of this new class of polymer micelles shed significant light on the structure and properties of the steady-state association colloids. Dynamics and out-of-equilibrium processes, such as (dis)assembly pathways, exchange kinetics of the micellar constituents, and reaction-assembly networks, have steadily gained more attention. We foresee that the broadened scope will contribute toward the design and preparation of otherwise unattainable structures with emergent functionalities and properties. This Viewpoint focuses on current efforts to study such dynamic and out-of-equilibrium processes with greater spatiotemporal detail. We highlight different approaches and discuss how they reveal and rationalize similarities and differences in the behavior of mixed micelles prepared under various conditions and from different polymeric building blocks.

Development of siRNA Therapeutics for the Treatment of Liver Diseases

Small interfering RNA (siRNA)-based therapeutics holds the promise to treat a wide range of human diseases that are currently incurable using conventional therapies. Most siRNA therapeutic efforts to date have focused on the treatment of liver diseases due to major breakthroughs in the development of efficient strategies for delivering siRNA drugs to the liver. Indeed, the development of lipid nanoparticle-formulated and GalNAc-conjugated siRNA therapeutics has resulted in recent FDA approvals of the first siRNA-based drugs, patisiran for the treatment of hereditary transthyretin amyloidosis and givosiran for the treatment of acute hepatic porphyria, respectively. Here, we describe the current strategies for delivering siRNA drugs to the liver and summarize recent advances in clinical development of siRNA therapeutics for the treatment of liver diseases.

Chemo-physical Strategies to Advance the in Vivo Functionality of Targeted Nanomedicine: The Next Generation

The past few decades have witnessed an evolution of nanomedicine from biologically inert entities to more smart systems, aimed at advancing in vivo functionality. However, we should recognize that most systems still rely on reasonable explanation-including some over-explanation-rather than definitive evidence, which is a watershed radically determining the speed and extent of advancing nanomedicine. Probing nano-bio interactions and desirable functionality at the tissue, cellular, and molecular levels is most frequently overlooked. Progress toward answering these questions will provide instructive insight guiding more effective chemo-physical strategies. Thus, in the next generation, we argue that much effort should be made to provide definitive evidence for proof-of-mechanism, in lieu of creating many new and complicated systems for similar proof-of-concept.

On Complex Coacervate Core Micelles: Structure-Function Perspectives

The co-assembly of ionic-neutral block copolymers with oppositely charged species produces nanometric colloidal complexes, known, among other names, as complex coacervates core micelles (C3Ms). C3Ms are of widespread interest in nanomedicine for controlled delivery and release, whilst research activity into other application areas, such as gelation, catalysis, nanoparticle synthesis, and sensing, is increasing. In this review, we discuss recent studies on the functional roles that C3Ms can fulfil in these and other fields, focusing on emerging structure-function relations and remaining knowledge gaps.

Smart Nanocarriers for the Delivery of Nucleic Acid-Based Therapeutics: A Comprehensive Review

Nucleic acid-based therapies are promising therapeutics for the treatment of several systemic disorders, and they offer an exciting opportunity to address emerging biological challenges. The scope of nucleic acid-based therapeutics in the treatment of multiple disease states including cancers has been widened by recent progress in Ribonucleic acids (RNA) biology. However, cascades of systemic and intracellular barriers, including rapid degradation, renal clearance, and poor cellular uptake, hinder the clinical effectiveness of nucleic acid-based therapies. These barriers can be circumvented by utilizing advanced smart nanocarriers that efficiently deliver and release the encapsulated nucleic acids into the target tissues. This review describes the current status of clinical trials on nucleic acid-based therapeutics and highlights representative examples that provide an overview on the current and emerging trends in nucleic acid-based therapies. A better understanding of the design of advanced nanocarriers is essential to promote the translation of therapeutic nucleic acids into a clinical reality.

The Arachno-Zintl Ion (Sn5 Sb3 )3- and the Effects of Element Composition on the Structures of Isoelectronic Clusters: Another Facet of the Pseudo-Element Concept

The pseudo-element concept, in its most general formulation, states that isoelectronic atoms form equal numbers of bonds. Hence, clusters such as Zintl ions usually retain their structure upon isoelectronic replacement of some or all atoms. Here, a deviation from this common observation is presented, namely the formation of (Sn5 Sb3 )3- (1), a rare example of an eight-vertex Zintl ion, and an unprecedented example of a Zintl ion synthesized by solution means that has an arachno-type structure according to the Wade-Mingos rules. Three structure-types of interest for (Sn5 Sb3 )3- were identified by DFT calculations: one that matched the X-ray diffraction data, and two that that were reminiscent of fragments of known clusters. A study on the isoelectronic series of clusters, (Snx Sb8-x )2-x (x=0-8), showed that the relative energies of these three isomers vary significantly with composition (independent of electron count) and that each is the global minimum at least once within the series.

Nanoparticle BAF312@CaP-NP Overcomes Sphingosine-1-Phosphate Receptor-1-Mediated Chemoresistance Through Inhibiting S1PR1/P-STAT3 Axis in Ovarian Carcinoma

Purpose

Platinum/paclitaxel-based chemotherapy is the strategy for ovarian cancer, but chemoresistance, inherent or acquired, occurs and hinders therapy. Therefore, further understanding of the mechanisms of drug resistance and adoption of novel therapeutic strategies are urgently needed.

Methods

In this study, we report that sphingosine-1-phosphate receptor-1 (S1PR1)-mediated chemoresistance for ovarian cancer. Then we developed nanoparticles with a hydrophilic PEG2000 chain and a hydrophobic DSPE and biodegradable CaP (calcium ions and phosphate ions) shell with pH sensitivity as a delivery system (CaP-NPs) to carry BAF312, a selective antagonist of S1PR1 (BAF312@CaP-NPs), to overcome the cisplatin (DDP) resistance of the ovarian cancer cell line SKOV3DR.

Results

We found that S1PR1 affected acquired chemoresistance in ovarian cancer by increasing the phosphorylated-signal transduction and activators of transcription 3 (P-STAT3) level. The mean size and zeta potential of BAF312@CaP-NPs were 116 ± 4.341 nm and −9.67 ± 0.935 mV, respectively. The incorporation efficiency for BAF312 in the CaP-NPs was 76.1%. The small size of the nanoparticles elevated their enrichment in the tumor, and the degradable CaP shell with smart pH sensitivity of the BAF312@CaP-NPs ensured the release of BAF312 in the acidic tumor niche. BAF312@CaP-NPs caused substantial cytotoxicity in DDP-resistant ovarian cancer cells by downregulating S1PR1 and P-STAT3 levels.

Conclusion

We found that BAF312@CaP-NPs act as an effective and selective delivery system for overcoming S1PR1-mediated chemoresistance in ovarian carcinoma by inhibiting S1PR1 and P-STAT3.

Development of lipid-like materials for RNA delivery based on intracellular environment-responsive membrane destabilization and spontaneous collapse

Messenger RNA and small interfering RNA are attractive modalities for curing diseases by complementation or knock-down of proteins. For success of these RNAs, a drug delivery system (DDS) is required to control a pharmacokinetics, to enhance cellular uptake, to overcome biological membranes, and to release the cargo into the cytoplasm. Based on past research, developing nanoparticles that are neutrally charged have been the mainstream of their development. Also, the materials are further mounted with pH- and/or reducing environment-responsive units. In this review, we summarize progress made in the molecular design of these materials. We also focus on the importance of the hydrophobic scaffold for tissue/cell targeting, intracellular trafficking, and immune responses. As a practical example, the design concept of the SS-cleavable and pH-activated lipid-like material (ssPalm) and subsequent molecular modification tailored to the RNA-based medical application is discussed.

Co-Delivery of Paclitaxel and Interleukin-12 Regulating Tumor Microenvironment for Cancer Immunochemotherapy

In the treatment of malignant tumors, the combination of chemotherapy that can directly kill tumor cells and immunotherapy that can activate the body's immune system and regulate tumor microenvironments is becoming one of the most promising cancer treatments. However, to co-deliver agents with different physicochemical properties for immunochemotherapy is still facing a challenge. Here, nanoparticles are developed for the co-delivery of the hydrophobic chemotherapeutic drug paclitaxel (PTX) and biomacromolecule interleukin-12 (IL-12) through the acid-sensitive material mPEG-Dlink_m -PDLLA and low-temperature expansion effect of Pluronic F127. The nanoparticles encrich in the tumor site, significantly inhibit the growth and metastasis of breast cancer cells 4T1, and prolong the overall survival of tumor-bearing mice. The underlying immune mechanism is further explored. The combination of PTX and IL-12 activates T lymphocytes and NK cells to release IFN-γ, selectively inhibits regulatory T cells and induces M1-type differentiation of tumor-related macrophages, thereby improving tumor immunosuppressive microenvironments. This study may provide an effective strategy for cancer immunochemotherapy through co-delivery of chemotherapeutic drug and immune cytokine by the facile thermo-sponge nanoparticles.

Reshaping Tumor Immune Microenvironment through Acidity-Responsive Nanoparticles Featured with CRISPR/Cas9-Mediated Programmed Death-Ligand 1 Attenuation and Chemotherapeutics-Induced Immunogenic Cell Death

Blocking immune checkpoints with monoclonal antibody has been verified to achieve potential clinical successes for cancer immunotherapy. However, its application has been impeded by the "cold" tumor microenvironment. Here, weak acidity-responsive nanoparticles co-loaded with CRISPR/Cas9 and paclitaxel (PTX) with the ability to convert "cold" tumor into "hot" tumor are reported. The nanoparticles exhibited high cargo packaging capacity, superior transfection efficiency, well biocompatibility, and effective tumor accumulation. The CRISPR/Cas9 encapsulated in nanoparticles could specifically knock out cyclin-dependent kinase 5 gene to significantly attenuate the expression of programmed death-ligand 1 on tumor cells. More importantly, PTX co-delivered in nanoparticles could significantly induce immunogenic cell death, reduce regulatory T lymphocytes, repolarize tumor-associated macrophages, and enhance antitumor immunity. Therefore, the nanoparticles could effectively convert cold tumor into hot tumor, achieve effective tumor growth inhibition, and prolong overall survival from 16 to 36 days. This research provided a referable strategy for the development of combinatorial immunotherapy and chemotherapy.

Current Aspects of siRNA Bioconjugate for In Vitro and In Vivo Delivery

Studies on siRNA delivery have seen intense growth in the past decades since siRNA has emerged as a new class of gene therapeutics for the treatment of various diseases. siRNA bioconjugate, as one of the major delivery strategies, offers the potential to enhance and broaden pharmacological properties of siRNA, while minimizing the heterogeneity and stability-correlated toxicology. This review summarizes the recent developments of siRNA bioconjugate, including the conjugation with antibody, peptide, aptamer, small chemical, lipidoid, cell-penetrating peptide polymer, and nanoparticle. These siRNA bioconjugate, either administrated alone or formulated with other agents, could significantly improve pharmacokinetic behavior, enhance the biological half-life, and increase the targetability while maintaining sufficient gene silencing activity, with a concomitant improvement of the therapeutic outcomes and diminishment of adverse effects. This review emphasizes the delivery application of these siRNA bioconjugates, especially the conjugation strategy that control the integrity, stability and release of siRNA bioconjugates. The limitations conferred by these conjugation strategies have also been covered.

Poly( N-isopropylacrylamide)-Based Polymer-Inducing Isothermal Hydrophilic-to-Hydrophobic Phase Transition via Detachment of Hydrophilic Acid-Labile Moiety

The polymerization of N-isopropylacrylamide (NIPAAm) with ionizable monomers results in pH-responsive lower critical solution temperature (LCST) polymer which works in an ionization-dependent manner. However, gradual ionization of the comonomer occurs at a broad pH range due to the electrostatic field generated by the polymers, limiting the extent of LCST shift in response to pH change. Furthermore, excess introduction of comonomer may dull phase transition behavior. Here, we report the development of an ionization-independent LCST polymer that exerts a sharp isothermal hydrophilic-to-hydrophobic phase transition in response to slight pH change. Our polymer has a poly(NIPAAm/2-aminoisoprpylacrylamide (AIPAAm)) (P(NIPAAm/AIPAAm)) backbone that retains the continuous structural similarity of N-alkyl groups for preserving phase transition sensitivity, and primary amine for forming hydrophilic acid-labile 2-propionic-3-methylmaleic (PMM) amide linkage. The PMM moiety improves the polymer's hydrophilicity and drastically increases the LCST. Detachment of the PMM moiety in response to mild acidic condition (pH < 6.8) lowers the LCST to that of original P(NIPAAm/AIPAAm), permitting isothermal pH-responsive phase transition. Utilizing this mechanism, P(NIPAAm/AIPAAm) modified with PMM amide linkage exhibits a sharp hydrophilic-to-hydrophobic transition at a physiological temperature (37 °C) and, strikingly, facilitates interaction with cultured cells. Most importantly, our polymer showed significantly higher accumulation within a solid tumor after systemic injection compared to conventional PNIPAAm, which may be due to its phase transition responding to slightly acidic tumor microenvironment. Thus, this study provides a novel polymer that offers delicate control of LCST and pH-responsiveness suitable for use in even fuzzy biological environments.

Bioresponsive polyplexes - chemically programmed for nucleic acid delivery

INTRODUCTION

The whole delivery process of nucleic acids is very challenging. Appropriate carrier systems are needed, which show extracellular stability and intracellular disassembly. Viruses have developed various strategies to meet these requirements, as they are optimized by biological evolution to transfer genetic information into host cells. Taking viruses as models, smart synthetic carriers can be designed, mimicking the efficient delivery process of viral infection. These 'synthetic viruses' are pre-programmed and respond to little differences in their microenvironment, caused by either exogenous or endogenous stimuli.

AREAS COVERED

This review deals with polymer-based, bioresponsive nanosystems (polyplexes) for the delivery of nucleic acids. Strategies utilizing pH-responsiveness, redox-responsiveness as well as sensitivity towards enzymes will be described more in detail. Systems, which respond to other endogenous triggers (i.e. reactive oxygen species, adenosine triphosphate, hypoxia), will be briefly illustrated. Moreover, some examples for combined bioresponsiveness will be presented.

EXPERT OPINION

Bioresponsive polyplexes are a smart way to facilitate programmed, timely delivery of nucleic acids to desired, specific sites. Nevertheless, further optimization is necessary to improve the still moderate transfection efficiency and specificity - also in regard to medical translation. For this purpose, precise carrier structures are desirable and stability issues of bioresponsive systems must be considered.

Block Copolymer Micelles in Nanomedicine Applications

Polymeric micelles are demonstrating high potential as nanomedicines capable of controlling the distribution and function of loaded bioactive agents in the body, effectively overcoming biological barriers, and various formulations are engaged in intensive preclinical and clinical testing. This Review focuses on polymeric micelles assembled through multimolecular interactions between block copolymers and the loaded drugs, proteins, or nucleic acids as translationable nanomedicines. The aspects involved in the design of successful micellar carriers are described in detail on the basis of the type of polymer/payload interaction, as well as the interplay of micelles with the biological interface, emphasizing on the chemistry and engineering of the block copolymers. By shaping these features, polymeric micelles have been propitious for delivering a wide range of therapeutics through effective sensing of targets in the body and adjustment of their properties in response to particular stimuli, modulating the activity of the loaded drugs at the targeted sites, even at the subcellular level. Finally, the future perspectives and imminent challenges for polymeric micelles as nanomedicines are discussed, anticipating to spur further innovations.

Covalent Strategies for Targeting Messenger and Non-Coding RNAs: An Updated Review on siRNA, miRNA and antimiR Conjugates

Oligonucleotide-based therapy has become an alternative to classical approaches in the search of novel therapeutics involving gene-related diseases. Several mechanisms have been described in which demonstrate the pivotal role of oligonucleotide for modulating gene expression. Antisense oligonucleotides (ASOs) and more recently siRNAs and miRNAs have made important contributions either in reducing aberrant protein levels by sequence-specific targeting messenger RNAs (mRNAs) or restoring the anomalous levels of non-coding RNAs (ncRNAs) that are involved in a good number of diseases including cancer. In addition to formulation approaches which have contributed to accelerate the presence of ASOs, siRNAs and miRNAs in clinical trials; the covalent linkage between non-viral vectors and nucleic acids has also added value and opened new perspectives to the development of promising nucleic acid-based therapeutics. This review article is mainly focused on the strategies carried out for covalently modifying siRNA and miRNA molecules. Examples involving cell-penetrating peptides (CPPs), carbohydrates, polymers, lipids and aptamers are discussed for the synthesis of siRNA conjugates whereas in the case of miRNA-based drugs, this review article makes special emphasis in using antagomiRs, locked nucleic acids (LNAs), peptide nucleic acids (PNAs) as well as nanoparticles. The biomedical applications of siRNA and miRNA conjugates are also discussed.

A modular assembly pH-sensitive charge reversal siRNA delivery system

Cationic lipids and polymers are the most common non-viral vectors for siRNA delivery; however, their intense positively charged character may give rise to serum-triggered aggregation, immune activation, inflammation stimulation and grievous toxicity.

Functional polymer-based siRNA delivery carrier that recognizes site-specific biosignals

Responsive molecular designs to specific biosignals in microenvironments endow site-specific functionalities with associated polymers. Thus, the construction of small interfering RNA (siRNA) carriers with functional polymers enables smart programs that are triggered by sequential biosignals in a pathway to the targeted cytosol for effective gene silencing. In this review, we explain rational strategies for the design of functional polymers with responsiveness to biosignals and describe the examples of smart carriers for siRNA delivery.